1. Field of the Invention
The present invention relates to mechanisms for mounting hydrostatic motors to the drive systems of hydrostatic-motor-driven vehicles. The invention also relates to hydrostatic motors used to drive a tracked vehicle.
2. Description of Related Art
Hydrostatic motors are commonly used to drive the tracks of tracked vehicles. The low-speed, high-torque output of hydrostatic motors permits them, in many cases, to be rotationally fixed directly to the driveshaft of a track without the need for intermediate gear reduction systems. Such a tracked vehicle includes a source of pressurized hydraulic fluid (such as an internal combustion engine and hydraulic fluid pump) that is selectively connected to the input and output ports of the hydrostatic motor(s) to propel the vehicle. Typically, one or more hydrostatic motors are connected to each of the vehicle's two parallel tracks.
Brakes are typically provided for such a tracked vehicle in order to selectively prevent the tracks from rotating. The brakes may be connected directly to the output shafts of each of the hydrostatic motors, which are, in turn, directly connected to the driveshafts and tracks of the vehicle. For safety, such brakes are typically passively-engaging brakes that only disengage when an active power source is applied to them. As a result, if the vehicle's power source fails, the brakes engage to prevent unintentional, uncontrolled movement of the disabled vehicle.
In addition to the regular brakes, when hydraulic fluid is not permitted to enter or exit the hydraulic fluid ports of the hydrostatic motors (typically when the motors are not being driven), the hydrostatic motors function like positive-displacement pumps and resist rotation. As a result, the hydrostatic motors function as additional braking mechanisms for the tracked vehicle.
It is sometimes necessary to pull or tow a tracked vehicle. For example, when a vital component fails, such as the power source, the tracked vehicle loses power and must be towed to a location where it can be repaired. Unfortunately, when the vehicle must be capable of being towed (i.e., when the power source fails), both the brakes and the hydrostatic motors passively resist the tracks' rotation. Further, forcefully rotating the tracks and thus the hydrostatic motors, such as is required when the conventional tracked vehicle is towed, tends to wear and damage the hydrostatic motors and hydraulic fluid system.
Systems have been developed to address the above deficiencies. For example, one conventional partial-disengagement system for hydrostatic motors allows the hydrostatic motors to be partially disengaged from the tracks of the vehicle to facilitate towing. This conventional system includes a combination of three required features. First, a release mechanism is provided for selectively releasing the brakes. However, if the release system is a passively-engaging system, a second power source must be provided so that the power source failure that necessitated the towing does not also prevent the brake release mechanism from functioning. Second, a system is provided for selectively retracting the pistons within the hydrostatic motors so that the piston rollers do not knock against the motor cams while the vehicle is being towed and the tracks and engaged hydrostatic motors are consequently rotated. Third, a bypass valve is provided for directly operatively linking the input and output ports of the motors. As the motors rotate and function as hydrostatic pumps, hydraulic fluid simply circulates through the motors. As the preceding description illustrates, the conventional partial-disengagement system is both complex to create and complicated to use. The system also requires additional components that increase the cost of manufacture and maintenance.
Accordingly, there is a need for a less complicated and lower cost method for disengaging a hydrostatic motor from a drive shaft, especially during a towing operation.